My GD has four cats, and acres of land for them to roam, she has a cat flap that was being used by other cats, (I thought her cats were throwing parties) She solved that problem by having the cats re-chiped and the flap fitted with a securing device that responds to the chips,only. That however does not prevent the cats from dragging in moles, mice, rabbits,pigeons, and on one occasion a coot. Some,nearly all of them, alive.The coot made a spectacular mess,GD having left the kitchen door open, and the coot ending after a violent struggle, on the top of the kitchen units.Nature is nature, but I don't particularly like the amount of livestock, cats are responsible for killing.I know that squirrels are egg eaters, magpies (look and act a bit like killer whales) and kill small birds and eat eggs, but cats seem to enjoy it too much. Well fed cats are just as responsible. It's something in their genetic makeup, not as bad as foxes perhaps or wolverines, but nevertheless worrying.